This invention relates generally to the field of aerospace structures and, more specifically, to landing gears.
For the majority of their operation, landing gears are used to support an aircraft while it is stationary on the ground. However, landing gears must also be able to support the aircraft when it is landing and moving on the ground. Thus, landing gears must be designed to support not only the weight of the aircraft, but also the additional forces generated when the aircraft lands and moves on the ground.
The position in which each landing gear, when deployed, places their associated wheel(s) relative to the aircraft is also important to the design of the landing gears because the wheel positions affect the operation of the aircraft on the ground. For example, if the main landing gears place their associated wheel(s) too close to the longitudinal centerline of the aircraft, the aircraft will easily tip over onto its side. As another example, because the center of gravity of the aircraft is usually forward of the main landing gears"" wheels, if the main landing gears place their associated wheel(s) too far aft on the aircraft, the aircraft will require large amounts of force to rotate upwards during takeoff, enlarging takeoff distances or horizontal control surfaces. Thus, landing gears must be designed to place the wheels in the appropriate position relative to the aircraft as well as support the aircraft during its different modes of operation on the ground.
In addition, the ability to stow the landing gears within the skin of the aircraft after takeoff is important in the design of many landing gears because it reduces the aerodynamic drag of the aircraft. Thus, having landing gears that are able to retract within the skin of the aircraft is often beneficial.
To accomplish the support, wheel positioning, and stowage objectives, most aircraft have the principal point at which each main landing gear pivotably couples to the aircraft forward of the appropriate deployed position for the associated wheel(s) and have the pivot axis of the landing gears parallel with the deployed orientation of the rolling axis of the associated wheel(s). In addition, aircraft usually have the center of each wheel located in a vertical plane that contains the principal point and is parallel to the longitudinal centerline of the aircraft.
Unfortunately, sometimes either the aircraft itself or another system in the aircraft, such as a weapons bay, dictates that the principal pivot points of the main landing gears should not be in the usual location. Thus, the main landing gears must be configured to couple to the aircraft at some other available location while still placing the associated wheel(s) in the appropriate position, which can present difficult support and stowage problems, or a sacrifice of aerodynamic performance and/or ground performance must be made, by not stowing the landing gears or by using less desirable wheel placements, respectively.
In accordance with the present invention, a landing gear is provided that substantially eliminates or reduces at least some of the disadvantages and problems associated with previously developed landing gears. Accordingly, in particular embodiments, the disclosed landing gear, when deployed, places the center of an associated wheel in a position that is forward and outboard of a principal point at which the landing gear pivotably couples to an airframe.
In certain embodiments of the present invention, the landing gear includes a trunnion and a wheel. The trunnion has at least one principal pivot point that is adapted to be pivotably coupled to an airframe to allow the trunnion to pivot about a principal trunnion pivot axis. The trunnion is operable to move between a deployed position and a stowed position by pivoting about the principal trunnion pivot axis. The wheel is rotatably coupled to the trunnion and has a rolling axis and a center, which is located forward of the principal pivot point when the trunnion is in the deployed position.
In other embodiments of the present invention, a method for using a landing gear is provided. The method includes pivoting a landing gear trunnion, which has a principal pivot point and a rotatably coupled wheel, relative to an airframe from a stowed position to a deployed position about a principal trunnion pivot axis, the center of the wheel being forward of the principal pivot point when the trunnion is in the deployed position. The method also includes dampening at least some of the forces applied to the wheel with a shock damper coupled to the trunnion and the wheel, the forces generating a first moment about the principal trunnion pivot axis. The method further includes generating a second moment about the principal trunnion pivot axis to counteract the first moment.
The present invention has several technical features and advantages. For example, in some embodiments, one advantage is the ability of a landing gear, when deployed, to place the center of a wheel associated with the landing gear forward of the principal point at which the landing gear pivotably couples to an airframe. Thus, the wheel may be placed in the appropriate position relative to the airframe even when the principal pivot point of the landing gear must be coupled to the airframe aft of the position where the center of the wheel is to be placed. As another example, in certain embodiments, an advantage is the ability of a landing gear, when deployed, to place the center of a wheel associated with the landing gear outboard of the principal point at which the landing gear pivotably couples to an airframe. Thus, the wheel may be placed in the appropriate position relative to the airframe even when the principal pivot point of the landing gear must be coupled to the airframe inboard of the position where the center of the wheel is to be placed. As a further example, in particular embodiments, an advantage is the ability of a landing gear, when deployed, to place the center of a wheel associated with the landing gear forward and outboard of the principal point at which the landing gear pivotably couples to an airframe. Thus, the wheel may be placed in the appropriate position relative to the airframe even when the principal pivot point of the landing gear must be coupled to the airframe aft and inboard of the position where the center of the wheel is to be placed. As another example, in certain embodiments, an advantage is the ability of a landing gear to be retracted into a stowed position within the skin of an airframe even when the principal point at which the landing gear pivotably couples to the airframe is inboard of the position at which the center of the wheel is to be placed upon deployment. Thus, the landing gear can still be retracted within the skin, which improves the aerodynamic characteristics of the aircraft.
The invention also has several useful technical features. For example, in several embodiments, the disclosed landing gear uses a locking member that is placed into tension when the aircraft is in contact with the ground. Using a locking member that is placed into tension provides a relatively strong locking mechanism and, moreover, allows the locking member to be composed of a series of links that can pivot relative to each other upon retraction of the landing gear, allowing the landing gear to be stowed in a relatively compact space. As another example, in particular embodiments, the disclosed landing gear has a relatively small number of components, allowing for easy manufacture, installation, and maintenance of the landing gear. As a further example, in several embodiments, the landing gear uses a box design for the trunnion, which reduces the weight of the landing gear with only a relatively modest decrease in strength.
Other technical features and advantages will be readily apparent to one of skill in the art from the following figures, description, and claims.